1. Field of the Invention
The present invention relates to a power supply for a magnetron, in particular but not exclusively for use with a magnetron powering a lamp.
2. Description of the Related Art
Known magnetron power supplies include a converter circuit comprising:                a converter adapted to be driven by a DC voltage source and produce an alternating current output, the converter having:                    a resonant circuit including an inductance and a capacitance (“LC circuit”) exhibiting a resonant frequency and            a switching circuit adapted to switch the inductance and the capacitance to generate a switched alternating current having a frequency greater than that of the resonance of the LC circuit;                        an output transformer for increasing the voltage of the output alternating current and        a rectifier and smoothing circuit connected to a secondary circuit of the output transformer for supplying increased voltage to the magnetron.Herein, we describe such a circuit as a “Magnetron, Switched Converter Power Circuit” or MSCPC.        
In known magnetron power supplies, the DC voltage source for the converter normally includes (for regulatory reasons) power factor correction (PFC), to enable it to exhibit substantially ohmic characteristics when connected to alternating current mains.
Both the PFC voltage sources and the converters, that is the PFC stages and the converter stages, are usually high frequency switching devices, that is they incorporate electronic switches switched at high frequency with respect to the mains frequency. Both stages have efficiency characteristics whereby under some operating conditions their efficiencies drop off.
The efficiency of the PFC stage drops off when it is operated to generate an increasingly high DC voltage. The efficiency of the converter stage drops of when it is operated at higher switching frequency, further from resonance of its components, and when generating less current than its maximum current.
The dichotomy of maximum PFC efficiency at lower voltage and maximum converter efficiency mitigates against overall power supply efficiency.